A SewerScan is recommended on any new home purchase you are considering, even new homes can have problems in their sewer lateral.  The main sewer line from the home to the city or private connection is the responsibility of the home owner and it is best you identify if any problems exist prior to closing escrow. It is often the unknown that can get you in trouble.  The reasons for even having a home inspection will uncover several things you did not know before.   The term better safe than sorry applies when it comes to your major systems of your home